In body-in-white structures, joining methods have traditionally relied on resistance-spot welding (e.g., in steel structures). Interest in alternative materials has increased as the automotive industry continues to focus on reducing the weight of vehicles to meet customer expectations on fuel economy and CAFE requirements. In the case of aluminum intensive vehicles and other mixed metal joining applications, problems associated with welding aluminum have led to the adoption of cold-formed joint technologies, such as clinching and self-piercing rivets (SPR) that are currently the most prevalent technique used for forming joints. One advantage of SPR technology is that it is a high production volume assembly process.
Clinch joints offer the potential of added cost savings. If parts are secured together with a clinch joint, the cost of a specialized rivet can be saved. However, clinch joints tend to be weaker than SPR joints because they do not have the same degree of interlock. The reduced strength of clinch joints limits the potential applications for clinch joints. There is a need for increased strength clinch in joints and SPR joints.
Another problem with clinch joints and self-piercing rivets is that the bottom layer of the assembly is thinned when the joint is formed and may result in the rivet or clinch joint breaking through the bottom panel causing a corrosion concern. Both clinch joints and self-piercing rivets can be more widely used if the potential for breakthrough can be reduced.
The above problems and other problems are addressed by this disclosure as summarized below.